Note This update is included with Service Pack 2 for Windows Server 2008.

For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591
(http://support.microsoft.com/kb/119591/
)
How to obtain Microsoft support files from online services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

What to consider before you upgrade

Upgrading from the Release Candidate to the release version

Saved state files are not supported between the Release Candidate (RC) and the release version of Hyper-V. All virtual machines should be shut down correctly before you install the release version of Hyper-V.

Note If you have already applied the release version of Hyper-V, virtual machines in a saved state will not start. Additionally, you will receive the following error message:

An attempt to initialize the virtual machine saved state failed.

To resolve this issue, select the "Delete Save State" option for each virtual machine that is currently in a saved state.

Snapshot files are not supported between the Release Candidate (RC) and release version of Hyper-V. All virtual machine snapshots should be deleted by using the "Delete Snapshot Subtree" option for each virtual machine.

Note After you delete the snapshots and after you shut down the virtual machines, the changes that exist in the snapshot files (.avhd files) will merge into the parent virtual hard disk file (.vhd).

This operation can take a while. To verify that the snapshots have merged into the parent virtual hard disk file, locate the snapshots, and then verify that no .avhd files exist.

Note The saved state and snapshot files are compatible if you are upgrading from Release Candidate 1 (RC1) to the release version of Hyper-V.

Upgrading from a prerelease version (beta version) of Hyper-V to the release version of Hyper-V

If you run virtual machines on a Hyper-V prerelease build, follow the steps that are described in the following Microsoft Knowledge Base article after you upgrade to the release version of Hyper-V:

949222
(http://support.microsoft.com/kb/949222/
)
Virtual machines that were created on the beta version of the Hyper-V role do not start after the Hyper-V role is updated to a later version